Power control systems are known generally. In analog control circuits, an amplifier output power is detected by a peak-detect circuit, which is coupled to an integrator. An output of the integrator controls the amplifier in a manner that tends to match the output of the peak-detect circuit with a reference signal to the integrator.
U.S. Pat. No. 4,458,209 entitled “Adaptive Power Control Circuit”, assigned commonly with the present application, discloses a dual band analog control loop having an integrator with a variable response time provided by switching first and second resistors of an RC time constant. The faster time constant applies to transient operation and the slower time constant to steady-state operation. See also, U.S. Pat. No. 5,697,074 entitled “Dual Rate Power Control Loop For a Transmitter”.
In digital control circuits, the peak detect circuit output is filtered and converted to a digital format before being input to a processor, which provides an output control signal based on a comparison of the digitized input signal with a reference signal. Like the analog control circuits discussed above, digital control circuits control the amplifier in a manner that tends to match the digitized peak-detect circuit signal with the reference signal. Digital processing however runs generally at a slower rate than the modulation rate of the peak-detect circuit signal so that variation of the envelope is tracked poorly or not tracked at all. Another limitation of known digital control circuits is that a D/A converter at the output of the processor is written initially with an estimated value, which requires knowledge of gain at the start of the transmit sequence for acceptable performance. The estimated value moreover is susceptible to variations in temperature, voltage, load and other conditions. U.S. Pat. No. 5,287,555 entitled “Power Control Circuitry for A TDMA Radio Frequency Transmitter”, the subject matter of which is incorporated by reference herein.
The various aspects, features and advantages of the present invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description of the Invention with the accompanying drawings described below.